The present invention relates to ceramic cutting tool materials particularly useful for machining of heat resistant alloys and particularly to such cutting tool materials in which monocrystalline silicon carbide whiskers are uniformly distributed in an alumina matrix.
U.S. Pat. No. 4,543,345 (Wei) discloses a material comprising a matrix selected from the group consisting of alumina, mullite and B.sub.4 C having homogeneously dispersed therein 5-60 vol % of silicon carbide whiskers said silicon carbide whiskers having a micro-crystalline structure and a size range of about 0.6 .mu.m in diameter and a length of 10-80 .mu.m with an average aspect ratio (length/diameter) of 75. Similar values are found in U.S. Pat. No. 4,961,757 (Rhodes). The latter patent discloses that these materials are useful for metal cutting.
It is generally understood that a high aspect ratio promotes the toughening mechanisms crack bridging and pull-out. See Baeck and Kim, "The Effect of Whisker Length on the Mechanical Properties of Alumina-SiC-Whisker Composites", J Of Mat Sci 24 (1989), p. 1589-1593; and Wadsworth and Stevens, "The Influence of Whisker Dimensions on the Mechanical Properties of Cordierete/SiC Whisker Composites", J of The European Cer Soc 9 (1992), p. 153-163.